JP2009214426A - Surface protective film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protective film capable of attaining sufficient releasability by adding a small amount of a silicone additive, which is low in migration of unreacted silicone to a self-adhesive surface. <P>SOLUTION: The surface protective film comprises a base material layer made of polyolefine and a self-adhesive layer laminated to the surface of the base material layer, and the base material layer includes polyethylene having polyorganosiloxane as a graft chain and polypropylene. Polyorganosiloxane of 1-5 wt.% is included to the polyolefine in the base material layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface protective film, and more particularly, to a surface protective film for surface protection used for preventing adhesion of dust to the surface of an adherend and damage to the surface of the adherend.

  Conventionally, for example, when various articles and members such as optical devices, metal plates, painted steel plates, resin plates, glass plates, etc. are transported, processed, or cured, dirt adheres to these surfaces or the surface is damaged. A surface protective film is used to prevent this.

This type of surface protective film is manufactured by, for example, applying a pressure-sensitive adhesive solution containing an elastomer or the like to a base material layer made of a synthetic resin or the like, or coextruding the base material layer and the pressure-sensitive adhesive layer. However, in recent years, the production of surface protective films using a coextrusion method that is highly superior in terms of productivity and environment has been increasing.
Further, a surface protective film is used for an optical member for a liquid crystal display which is growing rapidly. Some optical members have an uneven surface such as a prism sheet or a diffusion film. Therefore, when a surface protective film is attached to these uneven surfaces, it is necessary to form a pressure-sensitive adhesive layer having a higher adhesive force because the contact area cannot be obtained.

  Generally, the surface protective film is industrially manufactured as a wound body obtained by winding a long film in a roll shape, for example. In the surface protective film as such a wound body, when the wound body is unfolded, the outer surface protective film can be easily peeled off from the inner surface protective film, that is, the wound body is unwound. There is a strong demand for being easy. However, since the pressure-sensitive adhesive layer having strong adhesive force strongly adheres to the back surface of the base layer of the surface protective film on the inner side of the roll (the opposite side of the base layer to the pressure-sensitive adhesive layer lamination side, the same applies hereinafter) On the back surface of the base material layer of such a surface protective film, a release treatment that exhibits higher release properties than usual is required.

A surface protective film (for example, a base layer made of polyolefin resin and an adhesive layer are laminated by a co-extrusion method, and the back surface of the base layer is subjected to a friction treatment with a solid as a release-treated surface protective film (for example, Patent Document 1) has been proposed.
Further, an electron beam or γ is applied to the surface of the base material layer of the laminated sheet in which the base material layer composed of a polyorganosiloxane having one or more intramolecular double bonds and a polyolefin resin and the pressure-sensitive adhesive layer are laminated. A method for producing a surface protective adhesive sheet for irradiating a line has been proposed (Patent Document 2).
Furthermore, a surface protection sheet comprising a base material layer made of polyethylene having a polyorganosiloxane as a graft chain and an adhesive layer, and the surface of the base material layer is treated by irradiation with electron beams or γ rays. It has been proposed (Patent Document 3).

JP-A-2-252777 Japanese Patent Laid-Open No. 2-252783 Japanese Patent Laid-Open No. 2-252782

  The friction treatment with the solid on the back surface of the base material layer as in Patent Document 1 can be performed inline relatively easily. However, it is difficult to rewind the surface protection film having strong adhesive force only by the friction treatment, and problems such as deformation of the film occur during rewinding.

  Moreover, in the surface protection adhesive sheet of patent document 2, when the ratio of polyorganosiloxane with respect to polyolefin is 5 to 60 weight%, comparatively high mold release property is obtained. However, it is difficult to completely react in-line by irradiating a polyorganosiloxane having an intramolecular double bond with an electron beam or γ-ray. When an attempt is made to irradiate a higher energy electron beam or γ-ray, damage to the film increases and new problems such as embrittlement and yellowing occur.

  Further, in Patent Document 3, since the polyorganosiloxane is previously grafted, the migration of unreacted silicone, which has not been grafted, to the adhesive surface is relatively suppressed. However, the ratio of polyorganosiloxane to polyethylene is preferably 5 to 70% by weight, and the content of polyorganosiloxane is still large. In addition, in Patent Document 3, extraction using n-pentane and irradiation with electron beam or γ-ray are performed. However, actually, unreacted silicone also acts to increase the releasability. In the extraction using n-pentane, unreacted silicone and grafted low molecular weight polyethylene are extracted, and the releasability is greatly reduced. In addition, since the content of the polyorganosiloxane is still high, it is still difficult to completely react even when irradiated with an electron beam or γ-ray, and the remaining unreacted silicone moves to the adhesive surface (Patent Document 3). ).

  An object of the present invention is to provide a surface protective film that provides sufficient release properties by adding a small amount of a silicone additive and has little transfer of unreacted silicone to an adhesive surface in view of the current state of the prior art described above. Is to provide.

The surface protective film of the present invention is a surface protective film comprising a base material layer made of polyolefin and an adhesive layer laminated on the surface of the base material layer,
The base material layer contains polyethylene having a polyorganosiloxane as a graft chain and polypropylene, and the polyorganosiloxane content in the base material layer is 1 to 5% by weight.
This surface protective film is preferably formed by irradiating the back surface of the base material layer with an electron beam.

  The surface protective film of the present invention is considered to exhibit the release effect of polyethylene having polyorganosiloxane as a graft chain and the low molecular weight residue produced by the decomposition of polypropylene contained in the base material layer by electron beam irradiation. The mold release effect works additively, and sufficient releasability is achieved simply by irradiating the electron beam in-line, and because the amount of polyorganosiloxane contained in the base material layer is small, the residual due to low migration It is possible to achieve both securing of adhesive strength.

The surface protective film in the present invention comprises at least one base material layer and an adhesive layer.
The base material layer is made of polyolefin and contains at least polyethylene having a polyorganosiloxane as a graft chain and polypropylene.
The polyorganosiloxane introduced into polyethylene as a graft chain preferably has 6 or more polymerized units composed of an organosiloxane skeleton, more preferably 12 or more. Such polyethylene can be produced, for example, according to or according to the method described in JP-A No. 02-252782. Moreover, it is also possible to use a commercial item, for example, you may use the brand name "BY27-202H" by Toray Dow Silicone Co., Ltd. etc. as what grafted polydimethylsiloxane to polyethylene.

  The content of the polyorganosiloxane in the base material layer is preferably 1 to 5% by weight, and more preferably 1% by weight or more and less than 5% by weight. By setting this range, a sufficient release effect can be obtained, and the amount of unreacted silicone remaining after electron beam irradiation, etc. can be kept to a minimum, and the transfer of this component to the adhesive layer can be suppressed. can do.

  Polypropylene is not particularly limited, and any of homopolymer, block copolymer, and random copolymer may be used. Among these, it is preferable to use a homopolymer because releasability is improved and rewinding can be performed smoothly. The content of polypropylene is usually 10% by weight or more, preferably 30% by weight or more based on the total weight of the polyolefin constituting the substrate.

The base material layer may contain a polyolefin other than polyethylene and polypropylene having polyorganosiloxane as a graft chain.
The polyolefin to be used is not particularly limited, and ethylene-based polymers such as low density, high density, and linear low density polyethylene; propylene-based polymers such as block and random systems composed of a propylene component and an ethylene component; ethylene-α-olefin Examples include olefin polymers such as copolymers, olefin polymers of ethylene components and other monomers such as ethylene-vinyl acetate copolymers, ethylene-methyl methacrylate copolymers, and the like. These polyolefins may be used alone or in combination of two or more.

  The base material layer in the present invention may be a single layer of polyolefin containing polyethylene having a polyorganosiloxane as a graft chain and polypropylene as described above. The laminated structure of two or more layers arrange | positioned on the surface (namely, back surface) on the opposite side to the lamination | stacking side of the adhesive layer to perform may be sufficient. In this case, if the layer forming the back surface is simply referred to as the base material layer, and the layer disposed on the other side than the back surface is referred to as the intermediate layer, the intermediate layer is a material selected from the above-described polyolefins, that is, May be composed of only the above components, but at least one selected from thermoplastic resins such as polycycloolefin, polyester, polyamide, polyvinyl alcohol, ethylene-polyvinyl alcohol copolymer, or the like. You may use the blend of a material and the polyolefin-type component mentioned above. Especially, what contains polyolefin from the point of cost and a moldability is preferable.

  If necessary, other additives may be used in the above-described base material layer as long as the object of the present invention is not impaired. Examples of such additives include known light stabilizers such as ultraviolet absorbers, antioxidants, hindered amine light stabilizers, and antistatic agents. Furthermore, for example, known materials such as fillers such as calcium oxide, magnesium oxide, silica, zinc oxide, and titanium oxide, pigments, anti-scratch agents, lubricants, and anti-blocking agents can be appropriately blended as additives. .

Although it does not specifically limit as a material which comprises an adhesive layer, The adhesive composition which has a rubber-type resin component as a main component is used preferably.
As a rubber-type resin component, what is used as a base polymer of adhesives, such as a styrene-type elastomer, a urethane-type elastomer, an ester-type elastomer, an olefin-type elastomer, can be especially used without a restriction | limiting. In particular, when a styrene-based elastomer or an olefin-based elastomer is used, a surface protective film can be easily formed by coextrusion, and a surface protective film having good temporary adhesion to an adherend can be provided. .

  Specific examples of the styrene elastomer include styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene-butylene-styrene (SEBS), and styrene-ethylene-propylene-styrene (SEPS). ABA type block polymers such as styrene-isobutylene-styrene (SIBS); styrene-butadiene (SB), styrene-isoprene (SI), styrene-ethylene-butylene (SEB), styrene-ethylene-propylene (SEP) ), A-B type block polymer such as styrene-isobutylene (SIB); Styrene random such as styrene-butadiene rubber (SBR); ABC type such as styrene-ethylene-butylene-olefin crystal (SEBC) Styrene-Olef Emissions crystalline block polymers, and the like.

Examples of the olefin elastomer include CBC type olefin crystal block polymers such as olefin crystal-ethylene-butylene-olefin crystal (CEBC), ethylene-α-olefin, ethylene-propylene-α-olefin, propylene. -Alpha-olefin etc. are mentioned.
These rubber-based resin components may be used alone or in combination of two or more.

  When the rubber-based resin component has an unsaturated double bond derived from an olefin or a conjugated diene, the number of unsaturated double bonds is preferably smaller from the viewpoint of improving heat resistance and weather resistance. It is preferable that it is added. For example, in a styrene-based elastomer, at least 80% of double bonds of a conjugated diene moiety in a conjugated diene polymer block that is an olefin polymer block or in a random copolymer block of styrene and a conjugated diene that is an olefin. Is preferably saturated by hydrogenation, preferably 90% or more, and more preferably 95 to 100% saturated.

  The weight average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography) of the styrene elastomer is preferably in the range of 30,000 to 400,000, more preferably in the range of 50,000 to 200,000. This is because the cohesive force of the pressure-sensitive adhesive layer is ensured and adhesive residue on the adherend when the surface protective film is peeled off is prevented. Moreover, it is for ensuring a suitable adhesive force and preventing the increase in a solution viscosity or a melt viscosity at the time of preparation of an adhesive composition or manufacture of a surface protection film.

By using a tackifier as a material constituting the pressure-sensitive adhesive layer, the adhesive strength of the pressure-sensitive adhesive layer can be effectively increased. In this case, it is preferable to use the surface protective film in an amount that does not cause adhesive residue when peeling off the adherend. For example, the blending ratio of the tackifier is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, and still more preferably 10 parts by weight or less with respect to 100 parts by weight of the rubber-based resin component.
In general, the pressure-sensitive adhesive layer is preferably a single layer, but may have a laminated structure of two or more layers.

  Examples of the tackifier include petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic / aromatic copolymer systems and alicyclic copolymers, and coumarone-indene resins. Terpene resin, terpene phenol resin, process oil, castor oil, tall oil, natural oil, liquid polyisobutylene resin, polybutene, rosin resin such as polymerized rosin, (alkyl) phenol resin, xylene resin Or what is generally used for adhesives, such as these hydrogenated substances, can be especially used without a restriction | limiting. These tackifiers may be used alone or in combination of two or more. In order to improve the peelability and weather resistance, it is more preferable to use a hydrogenated tackifier. Moreover, you may use the tackifier marketed as a blend with an olefin resin.

For the purpose of controlling the adhesive strength, the pressure-sensitive adhesive layer can be appropriately mixed with known additives such as an ultraviolet absorber, an antioxidant, and an antiadhesive agent as necessary.
Examples of the adhesion progress preventing agent include fatty acid amides, polyethyleneimine long-chain alkyl grafts, soybean oil-modified alkyd resins (for example, Arakawa Chemical Co., Ltd., trade name “Arachid 251”), tall oil-modified alkyd resins (for example, Arakawa). Chemical name, “Arachid 6300”, etc.).
Other additives can be the same as those added to the base material layer described above.

The method for producing the surface protective film of the present invention is not particularly limited. For example, the substrate layer and the pressure-sensitive adhesive layer are laminated and integrated by co-extrusion by a known method such as an inflation method or a T-die method. Is preferable for exerting the effects of the present invention.
Moreover, the surface protection film of this invention is manufactured industrially as a wound body which wound the elongate film in roll shape, for example. When the surface protective film is a wound body, the pressure-sensitive adhesive layer is in close contact with the side of the substrate opposite to the side where the pressure-sensitive adhesive layer is formed. In the present invention, even in such a case, and when the surface protective film is, for example, a relatively wide wound body, the wound body can be easily rewound.

About 10-200 micrometers is suitable for the total film thickness of a surface protective film, 20-150 micrometers, Furthermore, 30-100 micrometers is more preferable.
The thickness of the substrate layer is not particularly limited, but is preferably about 5 to 180 μm, more preferably about 10 to 130 μm, and more preferably about 20 to 100 μm in consideration of handling properties, cost, and moldability.
Although the thickness in particular of an adhesive layer is not restrict | limited, It is about 0.5-30 micrometers, Preferably it is 1-20 micrometers, More preferably, it is 2-10 micrometers.

  In the present invention, it is preferable that the back surface of the base material layer in the surface protective film obtained by coextrusion is subjected to friction treatment and / or irradiation with an electron beam. The friction treatment of the back surface of the base material layer can be performed by a known method such as a method described in JP-A-2-252777 or a method analogous thereto. Specifically, a friction treatment using a rotating object such as a metal roll or a cloth such as gauze is exemplified. Thereby, the mold release effect resulting from some change of the resin which exists in the surface of a base material layer can be provided, and an expansion | deployment force can be made further smaller.

  Moreover, it is preferable that the electron beam irradiated to the back surface of a base material layer is 30-200 kV. If the accelerating voltage is too low, the releasability is insufficient, and if it is too high, the effect of irradiation other than the back surface appears, which may cause problems such as the base material layer becoming brittle and adhesive force changing. In addition, if the dose is too large, the base material layer and / or the pressure-sensitive adhesive layer is deteriorated, the base material layer becomes brittle, the residual adhesive force is reduced, and problems such as yellowing are likely to occur. Less than 100 kGy is suitable, preferably about 80 kGy or less, and about 60 kGy or less. Moreover, about 1 kGy or more is preferable.

  In the present invention, the electron beam irradiation is preferably performed uniformly on the back surface of the base material layer. As long as this is possible, the irradiation may be performed after the production of the surface protective film as described above, or only the base material layer. The surface opposite to the surface on which the pressure-sensitive adhesive layer is formed may be preliminarily irradiated with an electron beam, and then the pressure-sensitive adhesive layer may be formed on a surface that has not been irradiated with an electron beam. It may be performed at any stage before or after. That is, the friction treatment, electron beam irradiation, and formation of the pressure-sensitive adhesive layer may be performed in any order. Especially, when the simplification of a manufacturing method and the mold release process effect are considered, it is preferable to manufacture a surface protective film and to carry out a friction process after irradiating an electron beam with respect to the back surface of a base material layer.

  Hereinafter, examples of the surface protective film of the present invention will be described in detail. However, the present invention is not limited to the following examples.

Example 1
As a material for forming the base material layer, polyethylene having a polydimethylsiloxane as a graft chain (trade name: BY27) with respect to 100 parts by weight of block polypropylene (block PP, manufactured by Prime Polymer Co., Ltd., trade name “Prime Polypro J704LB”). -202H; Toray Dow Silicone Co., Ltd.) was used. The content of the polyorganosiloxane with respect to the polyolefin in the base material layer is 3% by weight.
Further, as a material for forming the intermediate layer, a material obtained by dry blending block PP and low density polyethylene (LDPE, manufactured by Prime Polymer Co., Ltd., trade name “Mirason M12”) by 50% by weight was used.

As a material for forming the adhesive layer, 100 parts by weight of a styrene-based elastomer (SEBS, manufactured by Kraton Polymer Co., Ltd., product number: G1657) made of a hydrogenated styrene-butadiene copolymer was used as a tackifier. A pressure-sensitive adhesive composition containing 5 parts by weight of 125 (manufactured by Arakawa Chemical Industry Co., Ltd.) was kneaded with a twin screw extruder and pelletized.
These materials are put into a co-extruder and co-extruded by a T-die method, and a surface protective film (width 700 mm) of base layer (thickness 6 μm) / intermediate layer (thickness 28 μm) / adhesive layer (thickness 6 μm) )
The back surface of the obtained surface protective film was irradiated with an electron beam so as to be 10 kGy.

(Example 2)
A film was formed in the same manner as in Example 1 except that 75 parts by weight of block PP and 25 parts by weight of LDPE were used instead of 100 parts by weight of block PP, and the electron beam was irradiated in the same manner.

(Comparative Example 1)
A film was formed in the same manner as in Example 1 except that 100 parts by weight of LDPE was used instead of 100 parts by weight of the block PP, and an electron beam was irradiated in the same manner.

(Comparative Example 2)
A film was formed in the same manner as in Example 1 except that the addition amount of polyethylene having polydimethylsiloxane as a graft chain was changed to 15 parts by weight, and was similarly irradiated with an electron beam.
The content of the polyorganosiloxane with respect to the polyolefin in the base material layer is 8% by weight.

(Evaluation)
(1) Self-back surface peeling force Each surface protection film was affixed on the flat acrylic board from the adhesive layer side. Moreover, what cut out each surface protection film to the magnitude | size of width 25mm x length 150mm was prepared separately.
Using the 2 kg rubber roller from the pressure-sensitive adhesive layer side, cut each surface protective film of Example and Comparative Example to the back surface of the surface layer of each surface protective film of Examples and Comparative Examples affixed to an acrylic plate to 2 m. Affixed at a rate of / min. Thereafter, pressurization was performed at 60 ° C. and 3 MPa for 20 minutes using a press machine, and this was left in a room at 23 ± 2 ° C. for 30 minutes. Thereafter, in accordance with JIS Z 0237, peeling between the surface protective films was performed, and the 180 degree peel strength at a width of 25 mm was measured at a speed of 30 m / min.

(2) Transferability Surface protection sampled from a wound body subjected to heat promotion treatment at 40 ° C. for 7 days after winding as a wound body against the adhesive strength A of the surface protective film sampled before winding as a wound body. The ratio (B / A) of the adhesive strength B of the film was evaluated. Each surface protective film was attached to a flat acrylic plate at a speed of 2 m / min from the pressure-sensitive adhesive layer side using a 2 kg rubber roller. This was left in a room at 23 ± 2 ° C. for 30 minutes. Thereafter, in accordance with JIS Z0237, the surface protective film was peeled off from the acrylic plate, and the 180 degree peel strength at 25 mm width was measured at a speed of 300 mm / min. The ratio of the adhesive strength was expressed as a percentage, and a case where it was 80% or more was judged as “◯”, a case where it was 60% or more and less than 80% was judged as “Δ”, and a case where it was less than 60% was judged as “X”.
The results are shown in Tables 1 and 2.

  The surface protective film of the present invention is not limited to various articles and members such as an optical device, a metal plate, a coated steel plate, a resin plate, and a glass plate, and it is necessary to prevent contamination and scratches during transportation, processing, or curing. It can be used for all adherends.

Claims (2)

A surface protective film comprising a base material layer made of polyolefin and an adhesive layer laminated on the surface of the base material layer,
The surface protective film, wherein the base material layer contains polyethylene having a polyorganosiloxane as a graft chain and polypropylene, and the polyorganosiloxane content in the base material layer is 1 to 5% by weight. .   The surface protective film according to claim 1, wherein the back surface of the base material layer is irradiated with an electron beam.